Export a polygon from an R plot as a shapefile

Question

I have been trying to export the content of a plot (lines/polygons) as a layer/shapefile that I can open in ArcMap. These are some of the libraries that I have been using,

library(shapefiles)
library(PBSmapping)
library(adehabitatHR)
library(maptools)
library(maps)
library(rgdal)
library(igraph)

My lat/long data looks like this:

tagdata<-read.table(text="meanlat  meanlong
-18.63327 147.0248
-18.6368  147.0238
-18.62068 147.294
-18.62953 147.2942
-18.62953 147.2942
-18.62091 147.2938
-18.62953 147.2942
-18.62466 147.2926
-18.73393 147.2816
-18.73393 147.2816
-18.75383 147.2541
-18.75383 147.2541
-18.75383 147.2541
-18.75383 147.2541
-18.6368  147.0238
-18.63063 147.0256
-18.63063 147.0256
-18.68133 147.1164
-18.6368  147.0238
-18.63063 147.0256
-18.63063 147.0256
-18.75383 147.2541
-18.61273 147.0682
-18.69655 147.09
-18.6368  147.0238
-18.63063 147.0256
-18.63063 147.0256
-18.63217 147.0251
-18.75383 147.2541
-18.75383 147.2541
-18.75383 147.2541
-18.63063 147.0256
-18.68133 147.1164
-18.68133 147.1164
-18.63217 147.0251
-18.69922 147.0909
-18.73393 147.2816
-18.63632 147.0792
-18.69522 147.0896
-18.6368  147.0238
-18.75383 147.2541
-18.75383 147.2541
-18.75383 147.2541",header=TRUE)

I plotted the locations and calculated the Minimum Convex Polygon (MCP) using the AdehabitatHR package.

plot(tagdata$meanlong,tagdata$meanlat, col="red",pch=1)                  

loc<-tagdata[ ,c("meanlong","meanlat")]
coord<-SpatialPoints(loc)
poly<-mcp(coord,percent=100)
plot(poly,add=TRUE)

I know how to export/write points as shapefile that I can open in ArcMap or similar softwares,

For example:

loc<-SpatialPoints(loc) # #convert loc to spatial points
rem<-tagdata[c(-1:-2)] 
SpatialPointsDataFrame(coords=loc,data=rem) 
obj<-SpatialPointsDataFrame(coords=loc,data=rem)
writePointsShape(obj,"myshape.shp")

However, I haven't found a good way to do it with a polygon o polyline object. I would loke to be able to export/write the poly object with the MCP as a shapefile. Any suggestions?

Solution

rgdal is superb for this kind of thing. http://www.gdal.org/ has most of the information you could every want on what formats are supported.

In this case you want the writeOGR function

# this will create a shapefile called poly within the working directory
library(rgdal)
writeOGR(poly, dsn = '.', layer = 'poly', driver = "ESRI Shapefile")

You could just as easily use it to write any shape file (point, polygon etc) but they must be SpatialxxxDataFrame objects

coorddf <-  SpatialPointsDataFrame(coord, data = data.frame(dummy = rep(1,nrow(coord@coords))))
writeOGR(coorddf, dsn = '.', layer = 'mypoints', driver = "ESRI Shapefile")

Comments

[mnel]

rgdal writeOGR

[Spacedman]

Obligatory Open Source Evangelism: Why are you using ArcMap? Why not try Quantum GIS? Or if you have further analysis to do, do it all in R!

[user1626688]

So how can I convert my Ploy<-MCP "object" that I plotted into SpatialxxxDataFrame. I know how to do it with points, but how can I do it with objects that don't really have a clear spatial reference?

[mnel]

Add an example of what you mean within your question

[mnel]

Your object poly is a SpatialPolygonsDataFrame

[mnel]

By SpatialxxxDataFrame i mean SpatialPointsDataFrame , SpatialPolygonsDataFrame or similar

[user1626688]

Got it! Thanks a lot! I was not sure if I need it an X/Y attribute table link to my polygon to export it as a shapefile.